The present invention relates generally to optical block assemblies, and more particularly to folded light path optical block assemblies.
Existing optical blocks for video cameras, such as closed circuit television (“CCTV) cameras, use a single linear optical path for light to enter the image sensor. For example, existing closed circuit television (“CCTV”) camera optical blocks are based on consumer electronics grade camcorder technology. In this technology, the image sensors are generally in the ⅓″ or ¼″ formats and the corresponding video format is of standard 768×494 pixel resolution for NTSC video signal format and 752×582 pixel resolution for PAL video signal format. A typical linear optical assembly 100 for existing CCTV products is shown in FIG. 1. As illustrated in FIG. 1, linear optical assembly 100 has a lens end 102 that includes a front lens 106, and a sensor end 104 that includes an image sensor 112 for receiving light gathered by lens 106. Also shown are zoom and focus lenses 120 and 122. The linear optical block configuration of assembly 100 forms a single linear optical path having a single longitudinal axis 101 between lens 106 and sensor 108. Linear optical assembly 100 is configured to swivel about a point 110, which is positioned near the center of gravity of linear assembly 100, to pan or tilt the assembly. Drawbacks associated with the configuration of such existing optical blocks include limitations on image sensor size, and rotational inertia associated with longer optical blocks and increased rotational speeds.
As image sensor resolution increases, the size of the sensor will typically increase. For example, typical CCTV resolution sensors have resolutions of 768×494 or 752×582 and have a diagonal size of either ¼″ or ⅓″. However, as resolutions increase to 1280×720 and beyond (e.g., to full High Definition Television—“HDTV” resolution), the image sensor size increases to the ½″ to ⅔″ range. This increase in size is due to the requirement to maintain overall sensitivity of the image element which is a function of size and light gathering capability. This sensitivity issue is most pronounced in camera applications where low light conditions are routinely encountered. While the linear arrangement of internal optical components may be acceptable for standard analog video resolutions, it is not possible to accommodate larger image sensors sizes without elongating the optical lens assembly. Extension of the optical block to accommodate larger sensor sizes results in larger housings, for example, requiring larger CCTV dome enclosures to house the optical block.
As the length of the optical block increases the rotational inertia required to pan and tilt the assembly also increase. This is true even if the optical block pivots at its center of gravity. This increased rotational inertia results in decreased efficiency from an electro-mechanical drive perspective. This problem is accentuated when increased rotational or pivoting speeds are desired, e.g., as desired by the CCTV video surveillance industry.